Our overall objective of this supplementary proposal is to extend our work on the nucleotide sequence analysis of DNA from simian virus 40 (SV40) and polyoma virus. Two new objectives are as follows: (a) To isolate and confirm the identity of a specific SV40 DNA-protein complex followed by the isolation of the SV40 DNA which is protected by this specific protein from nuclease digestion. Next, the nucleotide sequence of this isolated DNA segment will be analyzed. (b) To develop a new method for DNA sequence analysis based on the synchronous digestion of SV40 DNA with E. coli exonuclease III followed by repair synthesis and sequence analysis.